This invention relates to alternating current (AC) generator regulators and more particularly to a field regulation control and method utilizing a fixed frequency xe2x80x9cturn onxe2x80x9d and a set point xe2x80x9cturn offxe2x80x9d.
It is known in the art relating to alternating current (AC) generator regulators to use a pulse width modulation (PWM) scheme where the PWM is commanded by a non-linear algorithm to regulate the generator field. The algorithm is non-linear for load response reasons and to compensate for the non-linear response of the field and hence the generator. Non-linear here references the fact that a fixed current change (example 10 amps) will create a different transient depending on whether the generator is near full load or is near no load. A free wheeling diode is typically used to clamp the inductive energy of the field. This results in a faster or slower decay in the freewheel mode than the field charge mode depending on whether the field is at high or low current respectively. The average voltage applied to the field is proportional to B+, which can cause some instabilities because increasing B+ causes field voltage to increase which in turn increases B+.
Conventional regulators also have an overcurrent circuit which shuts down the output device for a finite period of time. This overcurrent circuit has caused some problems when the field resistance gets low which occurs when the generator is cold resulting in reduced generator output until the overcurrent condition goes away.
An object of the present invention is to reduce alternating current (AC) generator field regulation circuit complexity and improve generator regulator performance.
Another object of the invention is to eliminate the need for a non-linear control to compensate for the varying response at different loads to a fixed load step. Still another object is to eliminate the over current problem in conventional designs.
Yet another object of the invention is to eliminate the need for overvoltage protection.
Accordingly, a field regulation control and method are provided which uses current through the switch. A circuit configuration for controlling the field current of an alternating current generator in a vehicle electrical generator system includes a digital to analog converter for converting a digital command signal to an analog voltage. A first comparator compares the system field current with the converted analog voltage. A switched component, operatively connected to a power switch, is switchable in response to the comparator output. A frequency generator, operatively connected to the switched component, provides timed pulses to periodically tell the switched component to turn on the power switch.
The circuit configuration further includes a second comparator for comparing a sensed voltage, where voltage regulation is required, with a reference voltage. An up/down counter converts the over/under signal from the comparator to the digital command signal. A frequency generator increments the up/down counter. A supervisory control circuit is operatively connected to the up/down counter. Generator field and phase signals, and an ignition input signal are used to power up and power down the generator.
A method for controlling the field current of an alternating current generator in a vehicle electrical generator system includes:
converting a digital command signal to an analog voltage;
comparing the system field current with the converted analog voltage;
switching off a power switch in response to the comparator output; and
generating timed pulses to periodically tell the switched component to turn on the power switch.
The method further includes the steps of:
comparing a sensed voltage, where voltage regulation is required, with a reference voltage;
converting the over/under signal from the comparator to the digital command signal; and
incrementing the digital command signal.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.